Merge pull request #632 from fernandogrd/master

Fix processing of ManyToManyField when it is empty 

rest_framework/relations.py

@@ -148,7 +148,7 @@ class ManyRelatedMixin(object):
             value = data.getlist(self.source or field_name)
         except:
             # Non-form data
-            value = data.get(self.source or field_name)
+            value = data.get(self.source or field_name, [])
         else:
             if value == ['']:
                 value = []

rest_framework/tests/relations.py

@@ -31,3 +31,17 @@ class FieldTests(TestCase):
         field = serializers.SlugRelatedField(queryset=NullModel.objects.all(), slug_field='pk')
         self.assertRaises(serializers.ValidationError, field.from_native, '')
         self.assertRaises(serializers.ValidationError, field.from_native, [])
+
+
+class TestManyRelateMixin(TestCase):
+    def test_missing_many_to_many_related_field(self):
+        '''
+        Regression test for #632
+
+        https://github.com/tomchristie/django-rest-framework/pull/632
+        '''
+        field = serializers.ManyRelatedField(read_only=False)
+
+        into = {}
+        field.field_from_native({}, None, 'field_name', into)
+        self.assertEqual(into['field_name'], [])